At the New York Times, poll expert Nate Silver says Mitt Romney should make a play for Pennsylvania even if Barack Obama is atop all the surveys (and neither camp has been advertising here lately):
In Michigan, Romney's opposition to the auto bailout may be too much of an albatross. In Pennsylvania, though, the issue may be that while the polls are close, they are also hard to move; each party has its respective constituencies, and there may be few true undecided voters left. Obama's lead in Pennsylvania has often been narrow, but he has nevertheless led by some margin in the state's last 22 polls.
My calculations suggest that, despite Romney's deficit, the upside of his winning Pennsylvania is so great that he might want to take a chance. It's Obama's closest equivalent to a must-win state, and the combination of losing Pennsylvania and Ohio would essentially ensure his defeat. Unfortunately for Romney, it may be too late to adopt that strategy, as Obama has come close to clinching a majority of the state's electorate in recent surveys.